What are the types of rail bolts?

What Types of Rail Bolts Are Used in Track?

Rail bolts hold the track together: they clamp fishplates to the rail at joints, fix clips and base plates to sleepers, and secure switch and crossing components. The head design of each bolt is not a styling choice; it prevents the bolt from turning when the nut is tightened, and it stops the bolt working loose under vibration. Selecting the right bolt type for each position is part of every track specification.

Fish Bolts (Rail Joint Bolts)

Fish bolts clamp the fishplate (joint bar) to the rail web at bolted joints. The bolt passes through matching holes in the fishplate and the rail web, and the head shape is designed to stop rotation:

Diamond-neck (square-neck) bolts: the neck under the head is square and seats in the elongated hole of the fishplate, locking the bolt against rotation.

Oval-neck bolts: the neck is oval and seats in the corresponding hole profile; the oval is oriented so that the tightening torque only seats it more firmly.

Button-head bolts: a low round head used where head clearance is limited or where the fishplate has a countersunk seat.

Fish bolts are supplied with nuts and washers, and the length is matched to the fishplate thickness plus the rail web. On modern welded track, bolted joints survive mainly at insulated joints, switch ends and temporary installations.

T-Bolts

The T-bolt has a flat, T-shaped head that slides into a T-slot in the base plate or the switch plate. When the nut is tightened, the head jams against the slot walls and cannot turn. T-bolts are the standard fixing for rail base plates, switch plates and adjustable fastenings, and the head dimensions must match the slot of the plate exactly.

Clip and Clamp Bolts

Clip bolts and clamp bolts hold elastic rail clips or clamp assemblies down on the rail foot or base plate. Depending on the fastening system, the bolt may pass through the clip toe or through a clamp that presses the clip onto the rail. The important specification points are the thread size, the length, the strength class, and the torque applied at installation, because the clip toe load is set by that torque.

Anchor Bolts

Anchor bolts fix base plates, guard rails and other track furniture to the sleeper, or fasten the rail itself to steel girders on bridges and crane runways. On steel structures they are through-bolts with a counterplate or a weld-on stud; on concrete sleepers they are cast-in or resin-bonded studs. The bolt grade must suit the load and the corrosion environment.

Hook Bolts and Fang Bolts

Hook bolts are forged with a hook at one end that grips the underside of the rail foot or the edge of the sleeper, with the threaded end passing up through the base plate. They are used on timber sleeper track and on some bridge and crane installations. Fang bolts are a related family with sharp-edged fangs that bite into the timber to resist loosening.

Material and Strength Classes

Rail bolts are made from medium-carbon or alloy steel, usually heat-treated to a defined strength class. The property-class system of ISO 898-1 (equally used in GB/T 3098.1) covers them: class 4.8 for light-duty positions, class 8.8 as the standard for fish bolts and clip bolts on main lines, and class 10.9 where high clamping force is needed. The coating matters as much as the grade: hot-dip galvanizing for outdoor track, black oxide or zinc plating for protected positions, and special coatings where corrosion is severe.

Buyer Checklist

State the bolt type and head profile, not just the thread size.

Give the length, thread pitch and strength class on the order.

Match the neck profile to the fishplate or plate hole shape.

Specify the coating and require a test certificate for the strength class.

FAQ

What is a fish bolt used for?

A fish bolt clamps the fishplate (joint bar) to the rail web at bolted rail joints. Its shaped neck locks the bolt against rotation while the nut is tightened.

What is the difference between a T-bolt and a fish bolt?

A T-bolt has a flat T-shaped head that slides into a T-slot in a base plate, while a fish bolt has a diamond or oval neck that seats in the fishplate hole. They are not interchangeable.

What strength class are rail bolts?

Common classes are 8.8 for standard track bolts and 10.9 for high-clamping positions, per ISO 898-1 / GB/T 3098.1. Light-duty bolts may be class 4.8.

Why do fish bolts have shaped necks?

The diamond or oval neck seats in the matching hole of the fishplate and stops the bolt turning while the nut is tightened or under vibration, so the joint stays tight.

How should rail bolts be protected from corrosion?

Hot-dip galvanizing is standard for outdoor track. Zinc plating or black oxide is used in protected positions, and higher-performance coatings are specified in coastal or chemically aggressive environments.